1. Field of the Invention
The invention relates to an apparatus for medical diagnosis and/or therapy; including a detection device for electromagnetic detection of the presence of an object in the vicinity of a movable part of the apparatus, which detection device includes
a transmitter electrode which is connected to the movable part in order to produce an electromagnetic field in the vicinity of the transmitter electrode, PA1 a detection electrode which is connected to the movable part and arranged in the vicinity of the transmitter electrode in order to detect an electromagnetic field in the vicinity of the detection electrode, and PA1 a receiver which is arranged to receive on an input an input signal which corresponds to the electromagnetic field in the vicinity of the detection electrode, and to produce an output signal which corresponds to the input signal.
2. Description of the Related Art
An apparatus of this kind is known from German published Patent Application DE 41 26 168.
An apparatus for medical diagnosis and/or therapy may include a radiation transmitter and a radiation receiver. An example in this respect is a medical X-ray apparatus which includes an X-ray source and an X-ray detector which is usually referred to as an image intensifier. These two elements are arranged at some distance from one another, the patient to be examined or treated being positioned between the X-ray source and the image intensifier. The X-ray source and the image intensifier are positioned relative to the body of the patient in such a manner that an image can be formed of the desired slice of the body (the "object"). The orientation and position of such apparatus can often be adjusted by means of a motor drive. Generally speaking, in the context of the present invention an object is to be understood to mean the body of a patient to be examined, or an object to be examined otherwise, the body or a part of the body of a person attending the apparatus, parts of the apparatus itself (for example, the patient table) or of neighboring apparatus, or other obstacles which could invade the path of movement of the parts of the apparatus.
Many of such apparatus include a so-called C-arm, i.e. a circular carrier which is rotatable in its own plane (i.e. about an axis extending perpendicularly to the plane in which the C-arm is situated) by way of a guide (trackway) and whose own plane is rotatable about an axis situated in that plane. Moreover, often a number of other possibilities for displacement are provided.
During use of the apparatus it is important that a movable part, for example the image intensifier, closely approaches the object to be examined in order to achieve the desired clarity of the image. The image intensifier has a comparatively large front face for receiving the X-rays and each point on this front face or on its circumference can come into contact with the object to be examined. Such a collision can occur in any direction of movement of the image intensifier. This is undesirable and, therefore, such an apparatus includes a detection device for detecting the presence of an object in the vicinity of the movable part of the apparatus. It is important to provide such a detection device notably in the case of motor-driven apparatus. When an object is detected within a given small distance from the movable part of the apparatus, the movement of (that part of) the apparatus can be stopped so as to avoid a collision.
The cited Patent Application DE 41 26 168 discloses a medical X-ray apparatus which includes an electromagnetic collision sensor enabling detection of the presence of an object within a given, small distance from the movable part of the apparatus. This apparatus includes a signal source for producing an electric signal in the form of a fixed voltage. This voltage is applied to a transmitter electrode in the form of a metal foil. In the vicinity of the metal foil, but electrically insulated therefrom, there is provided a further metal foil which acts as a detection electrode. Between these two metal foils a signal can be measured which corresponds to the electromagnetic field strength in the vicinity of the collision sensor. This signal is further processed by means of a receiver which consists of a number of amplifiers and produces an output signal corresponding to the field strength.
It is desirable that during use of such an apparatus it can be checked that the electrodes and the electronic circuits for signal processing operate correctly. Therefore, in the known collision sensor the voltage from each of the electrodes is applied to a comparator associated with the relevant voltage, the voltage being compared therein with a slightly lower reference voltage. If the voltage from the relevant electrode is absent, the comparator outputs an output signal whose logic value opposes the value of the output signal in the situation in which the voltage from the relevant electrode is present. The output voltages of the comparators are applied to a logic circuit in order to establish the existence of a fault. This method of checking the correct operation of the electrodes and the electronic circuits has the drawback that it requires additional electronic circuits which themselves may also be subject to faults. Consequently, on the one hand the failure of an electrode may thus remain undetected whereas on the other hand a signal representing a fault can be produced even in the case of correct operation of the electrodes. The reliability of the detection device of the apparatus for medical diagnosis and/or therapy is thus adversely affected.
It is an object of the invention to provide an apparatus of the kind set forth in which incorrect operation of the electrodes and/or the electronic circuits coupled thereto can be more reliably detected.
To this end, the apparatus according to the invention is characterized in that the detection device includes a test electrode which is connected to the movable part and is arranged in the vicinity of the transmitter electrode and the detection electrode, a controllable switch which is connected between the test electrode and a point carrying a fixed voltage, and a control unit for controlling the state of conductivity of the switch.
In normal operating conditions the controllable switch is in the non-conductive state. When information is desired concerning the operation of the electrodes and the associated electronic circuits, the switch is set to the conductive state by means of the control unit for controlling the state of conductivity of the switch. The test electrode is thus connected to the point of fixed voltage so that the electromagnetic field in the vicinity of the electrodes exhibits the same change as if an obstacle were present in the vicinity of the movable part of the apparatus. The presence of an obstacle is thus simulated by driving the switch to the conductive state. By observation of the output signal produced by the receiver for receiving a signal corresponding to the electromagnetic field in the vicinity of the detection electrode it can be checked whether the output signal corresponds to the situation in which an obstacle is present. If this is not the case, it is practically excluded that the cause lies outside the electrodes or the electronics.
Further embodiments of the invention are disclosed in the dependent claims.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.